Support of tube walls

ABSTRACT

A buckstay system for supporting and reinforcing the tubular walls of a vapor generator including a grid adjacent to the walls and means permitting vertical and horizontal movement between the grid and the adjacent wall along the plane thereof.

llnite States Patent [191 Bijmholt [451 June 4,1974

[ SUPPORT OF TUBE WALLS [75] Inventor: Hans Bijmholt, Duisburg, Germany[73] Assignee: Babcock & Wilcox Limited, London.

England [22] Filed: July 13, 1973 [21] Appl. No.: 379,050

[52] US. Cl. 122/6 A, 122/510 [51] int. Cl. F22b 37/24 [58] Field ofSearch 122/6 A, 235 A, 494, 510

[56] References Cited UNITED STATES PATENTS 3,277,870 10/1966 Reale122/510 X Boe et a1 122/510 Stalph 122/6 Primary Examiner-Kenneth W.Sprague Attorney, Agent, or Firmloseph M. Maguire; Robert J. Edwards[57] ABSTRACT A buckstay system for supporting and reinforcing thetubular walls of a vapor generator including a grid adjacent to thewalls and means permitting vertical and horizontal movement between thegrid and the adjacent wall along the plane thereof.

4 Claims, 5 Drawing Figures SUPPORT OF TUBE WALLS BACKGROUND OF THEINVENTION This invention relates to support arrangements for vaporgenerators and more particularly to an arrangement permitting horizontaland vertical thermal expan sion of a top-supported vapor generator.

The support arrangement associated with a topsupported vapor generatorcomprises ground supported upright structural steelwork and cross beamsassociated with the upper portion thereof and including hangersdepending from the cross beams to provide support for the vaporgenerator and associated components. As the vapor generator is broughtup to operating temperature, the tubes associated therewith undergohorizontal and vertical thermal expansion, the latter being from a fixedreference point at the top of the vapor generator and being cumulativeso as to resalt in as much as inch movement at the bottom of a very tallutility type vapor generator.

The walls associated with the vapor generator are formed by upwardlyextending parallel tubes having their intertube spacing closedthroughout substantially all of their length by metallic webs welded toadjacent tubes to provide a gas-tight construction. this type ofconstruction is commonly known as a membrane wall.

The strength of a membrane wall is limited and is generally not capableof withstanding the weight of the support arrangement required tomaintain its integrity. The membrane wall support arrangement comprisesa framework disposed in surrounding relationship to the vapor generatorand includes a plurality of horizontal buckstays linked to verticalsupport beams with the latter being suspended from the structural steelcross beams through appropriate hangers. A plurality of connectingmembers are employed in linking the membrane walls to the verticalsupport beams and associated buckstays. The ends of each of theconnecting members is formed with a clevis which is in turn linked tothe adjoining structure. be it a tie-bar associated with the membranewall or one of the vertical support beams or the buckstay associatedtherewith.

Herctofore the arrangement of clevis type connecting members hasrequired the use of bolts having an axial length greater than themaximum vertical thermal expansion of the vapor generator and of adiameter structurally compatible with this length, i.e. 29 inch lengthand 2% inch diameter. It is the object of this invention to provide anarrangement which would replace the aforementioned bolt with one havingapproximate dimensions of 3% inch length and l inch diameter.

SUMMARY OF THE INVENTION In accordance with the present invention animprovement is made on clevis type connecting members associated with atop-supported vapor generator eliminating the requirement that boltsassociated therewith have an axial length exceeding the maximum lengthof vertical thermal expansion of the vapor generator associatedtherewith and corresponding to the level at which the connecting memberis applied.

The improvement comprises a retaining member having a C-shapedcross-section which is welded either to one of the vertical supportbeams or one of the membrane wall tie-bars. The retaining member is thusformed with a T-slot extending along the longitudinal length thereofandarranged to receive the base portion of the clevis-end of acorresponding connecting member. The longitudinal extent of the T-slotis parallel to the axis of the clevis bolt and the retaining member isdisposed so as to rigidiy restrain the clevis associated therewith inall directions perpendicular to the axis of the bolt thereby allowingthe connecting members to be loaded in tension or compression.

The retaining member may be manufactured by weldably joiningappropriately sized elongated flat plate strips to form a C-shapedcross-section configuration which engages the base portion of one of theclevises associated with a connecting mem her in such fashion as toallow vertical movement within the retaining member. The clevisassociated with the other end of the aforementioned connecting member isweldably attached to an adjacent tie-bar which is in turn rigidlyconnected to the membrane wall. The tie-bar is disposed contiguous tothe wall and is rigidly held thereon by clamps each of which comprises apair of scalloped bars welded to the membrane wall and accommodating arestraining pin extending therethrough and over the tie-bar. In thismanner. tensile and compressive stresses are distributed over a widerarea of the membrane wall while at the same time avoiding additionalstresses which may be generated by a differential in thermal expansionbetween the wall and the associated tie-bar.

Furthermore, the weight of the support arrangement is transmitted to theground-supported structural steelwork and not to the membrane wall.

At some locations of the vapor generator. i.e. the ends of thehorizontal buckstays associated with the surrounding wall supportframework. the arrangement is such that the buckstay is rigidly attachedto the clevis end of a corresponding connecting member while theopposite clevis end is slidably engaged with the retaining member ofavertical support beam in accordance with the invention. the verticalbeam being in turn weldably attached to a gusset plate and the latterbeing weldably attached to a corresponding tie-bar.

The present invention results in considerable simplification ofmanufacture in that all the support elements are of substantially thesame construction and have substantially the same dimensions whetherrigidly connected at the membrane wall or at the buckstay;

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 5 is a detail side elevationtaken along line D-D of FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 illustrates atop-supported upright furnace chamber 1 comprising fluid heating tubesarranged to form a gas-tight boundary. The furnace chamber 1 is ofsubstantially rectangular cross-section and is defined by two pairs ofopposed membrane walls 2 wherein the lower end of one of the pairsslopes inwardly to form a furnace hopper, and the upper portion of oneof the walls formed with an opening discharging into a gas passage (notshown). The membrane walls 2 are provided with tie-bars 3 rigidlyattached to the outside of the walls. The vapor generator and furnacechamber associated therewith are suspended from groundsupportedstructural steelwork including upright columns and cross beams 5. Thetie-bars 3 are rigidly connected to the cross beams 5 so as tosupportedly connect the membrane walls to the structural steelwork whilepermitting downward vertical movement resulting from thermal expansion.A furnace hopper support system 4 is attached to the tie-bars 3 andmoves with it in response to thermal expansion.

The wall support arrangement associated with the furnace chamberincludes a plurality of vertically spaced horizontal buckstays 6disposed around the chamber 1 and laterally spaced from the walls 2. Thebuckstays 6 have the primary function of providing lat eral support forthe membrane walls. however they may also serve as walkways around thefurnace chamber 1. The buckstays 6 are connected to a plurality ofvertical support beams 7 which are preferably l-beams. The support beams7 are uniformly spaced about the outer periphery of the furnace and aresupportedly connected to the structural steelwork by hanger rods 8depending from the cross beams 5.

During the operation of the vapor generator, the membrane walls 2 attainan elevated temperature and in turn heat up the tie-bars 3. This rise intemperature causes a downward thermal expansion in the direction ofarrow E relative to the vertical support beams 7 which remain generallyat ambient temperature. This downward thermal expansion is cumulativeand will, in

the case of a very tall vapor generator. result in a bottom movement ofapproximately 25 inches. The connecting members 21 linking the tie-bars3 to the vertical support beams 7 must be capable of transmittinghorizontal tensile and compressive forces of up to 2% tons per memberfrom the membrane wall 2 to the support beams 7 while at the same timepermitting the walls to thermally expand in the direction of arrow E.

As shown in FIGS. 3 and 4, each connecting member 21 consists of adouble flange contral portion 9 being formed with a clevis portion 10 atone end thereof and a clevis portion 11 at the other end thereof andincluding a bolt 12 associated with each of the clevises. Thelongitudinal axes of the bolts 12 of a respective connecting member 21are disposed parallel to one another. ln accordance with the inventionthe clevis 10 is rigidly connected to the tie-bar 3, preferably bywelding, while the tie-bar itself is rigidly held onto the membrane wall2 by a clamping arrangement consisting of a pair of scalloped plates 13straddling the tie-bar and a pair of retaining rods 14 extending throughthe plates 13 and over the tie-bar 3; the plates 13 being weldablyattached to the membrane wall 2. The clevis 11 is attached to acorresponding vertical support beam 7 in such manner as to prevent itsmovement in any horizontal direction while permitting it to slide in avertical direction. This is accomplished by providing the clevis 11 witha base portion 15 which fits into a C-shaped slot 16 formed by aretaining member 17, the latter being weldably attached to the supportbeam 7.

An alternate arrangement is shown in FIGS. 2 and 5 wherein the buckstays6 have their respective ends anchored through the use of connectingmembers 21' having central portions 9' and including clevises l0 and 11'and bolts 12' associated therewith. The base portion 15 of each of theclevis brackets 11' is inserted into the vertical groove or slot 16fitted on the support beam 7 so that the clevis 11 is free to slide in avertical direction. The vertical support beams 7 are weldably attachedthrough respective gusset plates 18 to the tiebars 3 thereby providing arigid connection to the corresponding membrane wall 2. This alternatearrangement of connecting members 21' is used to anchor the buckstays 6and allows the forces shown as arrow F to be transmitted to the membranewall 2 along a wide area and through the support lugs 19 to be therebydivided into smaller anchor forces as shown by arrow G.

It should be noted that the bolt and clevis arrangement associated withthe connecting members 21 permits unrestrained horizontal thermalexpansion in a direction parallel to the planar surface of the membranewall while providing the means for transferring from the wall to thebuckstays those forces which are due to tension and compression andwhich act in a direction normal to the planar surface of the membranewall. The vertical thermal expansion is compensated for through thesliding arrangement between the selected clevis base portion 15 and theretaining member 17 associated therewith. During start-up of the vaporgenerator all connecting members 21 move in a downward direction asshown by arrow E in FIG. 3 along with the membrane wall to which theyare rigidly attached. As the membrane wall 2 expands downward. the baseportion 15 of clevis ll moves in the direction of arrow E with its edgessliding within the slot 16 while also transferring the horizontaltensile and compressive forces from the wall through the verticalsupport beams 7 to the horizontal buckstays 6.

The ends of the buckstays 6 are provided with stressfree compensationwith respect to the differential in thermal expansion at the anchoringpoints by virtue of the sliding provision between the connecting members21' and corresponding support beams 7 in the direction of arrow E asshown in FlG. 5. Each of the clevises 10' is rigidly attached to acorresponding buckstay 6 while each of the clevises 11' is slidablyengaged with a corresponding member 7' through the clevis base portion15' and the retaining member slot 16.

During the cooling of the boiler a stress-free contraction takes placein a direction opposite to that of arrow E. During steady stateconditions whether cold or hot, the dirferences in thermal expansion arefully compensated.

While in accordance with the provisions of the statutes there isillustrated and described herein a specific embodiment of the invention,those skilled in the art will understand that changes may be made in theform of the invention covered by the claims, and that certain featuresof the invention may sometimes by used to advantage without acorresponding use of the other features.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

l. A fluid heating unit comprising a pair of spaced upright wallsdefining therebetween a chamber for the flow of heating gases, abuckstay system disposed outside of the chamber and means connecting thebuckstay system to said walls for lateral support and reinforcementthereof, a rigid support structure extending above said chamber, supportmembers separately connecting the walls and the buckstay system forpendent support therefrom, the buckstay system and the walls beingsubject to different rates of linear thermal expansion, said buckstaysystem including a grid adjacent each of said walls, each of the gridsincluding at least one horizontal structural member and at least onevertical structural member, said vertical member being disposed betweenthe horizontal member and the adjacent wall, and said connecting meansincluding a plurality of elongated members at least one of which has oneend rigidly connected to the adjacent wall and the other end slidablyengaged with the vertical member to permit relative vertical movementbetween the grid and the adjacent wall along the plane thereof.

2. A fluid heating unit according to claim 1 wherein the remaining ofsaid elongated members have one end rigidly connected to the horizontalmember and the other end slidably engaged with the vertical member.

3. A fluid heating unit according to claim 1 wherein each of the ends ofeach of the elongated members includes a pin and clevis arrangement topermit relative horizontal movement between the grid and the adjacentwall along the plane thereof.

4. A fluid heating unit according to claim 3 wherein the clevis includesa base portion and the vertical member is provided with a retaining clipfor engaging said base portion.

1. A fluid heating unit comprising a pair of spaced upright wallsdefining therebetween a chamber for the flow of heating gases, abuckstay system disposed outside of the chamber and means connecting thebuckstay system to said walls for lateral support and reinforcementthereof, a rigid support structure extending above said chamber, supportmembers separately connecting the walls and the buckstay system forpendent support therefrom, the buckstay system and the walls beingsubject to different rates of linear thermal expansion, said buckstaysystem including a grid adjacent each of said walls, each of the gridsincluding at least one horizontal structural member and at least onevertical structural member, said vertical member being disposed betweenthe horizontal member and the adjacent wall, and said connecting meansincluding a plurality of elongated members at least one of which has oneend rigidly connected to the adjacent wall and the other end slidablyengaged with the vertical member to permit relative vertical movementbetween the grid and the adjacent wall along the plane thereof.
 2. Afluid heating unit according to claim 1 wherein the remaining of saidelongated members have one end rigidly connected to the horizontalmember and the other end slidably engaged with the vertical member.
 3. Afluid heating unit according to claim 1 wherein each of the ends of eachof the elongated members includes a pin and clevis arrangement to permitrelative horizontal movement between the grid and the adjacent wallalong the plane thereof.
 4. A fluid heating unit according to claim 3wherein the clevis includes a base portion and the vertical member isprovided with a retaining clip for engaging said base portion.